1. Field of the Invention
The present invention relates to a method for connecting a wiring arranged on a sheet with another wiring arranged on another sheet by applying ultrasonic waves and pressure, and, in particular, to a method for connecting wirings arranged on wiring sheets which are put in electronic apparatus such as an audio visual apparatus and an office automation apparatus.
2. Description of the Related Art
Electronic apparatus such as an audio visual apparatus and an office automation apparatus has been recently miniaturized, and the electronic apparatus has recently become light in weight. Therefore, the electronic apparatus can be carried. In contrast, a large number of electronic parts and mechanical parts have been provided to the electronic apparatus at tight packing to fulfill many types of functions. Accordingly, a thin and lightweight type of flexible printed wiring sheet has been recently utilized to print an electronic wiring network to which the electronic parts and the mechanical parts are connected.
Also, the electronic apparatus has become cheap. Therefore, the electronic apparatus must be manufactured at a lower cost. To manufacture the electric apparatus at a lower cost, an electronic wiring network which are printed on the flexible printed wiring sheets or are formed on the wiring boards must be connected at a lower cost.
Conventionally, many types of discrete electronic parts and mechanical parts are directly attached on a single flexible printed wiring sheet so that the sheet is complicated in shape. In this case, the flexible printed wiring sheet is arranged in a narrow opening formed between the parts and an apparatus case accommodating the parts. Therefore, the discrete electronic parts are electrically connected through an electronic wiring network printed on the flexible printed wiring sheet.
Accordingly, even though the electronic parts and the mechanical parts are put in the apparatus case at tight packing, because the flexible printed wiring sheet is thin, the parts can be electrically connected through the electronic wiring network printed on the flexible printed wiring sheet to operate the parts in the equipment case. Also, because the flexible printed wiring sheet is light in weight, the electronic apparatus in which the parts are electrically connected with the electronic wiring network printed on the sheet can be easily carried. In addition, because the sheet is flexible, the sheet can be arbitrarily arranged at a desired position of the equipment case so that the electronic apparatus can be arbitrarily designed.
However, as the electronic apparatus is miniaturized, and as a large number of parts are put in the electronic apparatus at tight packing, the flexible printed wiring sheet becomes more complicated in shape. Also, when a designer requires to arbitrarily design the arrangement of the parts in the electronic apparatus, the flexible printed wiring sheet is more complicated in shape. In this case, because the flexible printed wiring sheet is complicate in shape, the number of the flexible printed wiring sheets cut out from a prescribed size of work sheet is reduced. That is, the flexible printed wiring sheet cannot be efficiently produced. Therefore, there is a drawback that the electronic apparatus cannot be manufactured on a large scale.
Also, after the flexible printed wiring sheet is cut out from the work sheet, it is difficult to handle the flexible printed wiring sheet because the sheet is complicated in shape. Therefore, there is another drawback that the electric apparatus cannot be efficiently manufactured.
To solve the above drawbacks, there is another conventional method in which the complicated shape of flexible printed wiring sheet is divided to a simple shape of many flexible printed wiring sheets. That is, many flexible printed wiring sheets being simple in shape are cut off from the work sheet, and an electronic wiring network is printed on each of the wiring sheets. Thereafter, the simple shape of flexible printed wiring sheets are mechanically connected with one another to electrically connect the electronic wiring networks. Thereafter, the simple shape of flexible printed wiring sheets are arranged in a complicated shape of opening formed between discrete electronic parts. Therefore, the electronic parts and the mechanical parts in the equipment case are electrically connected through the simple shape of flexible printed wiring sheets.
According to circumstances, a stiff type of wiring board is connected with the flexible printed wiring sheet to electrically connect electronic wiring networks in the equipment case.
To connect the simple shape of flexible printed wiring sheets, the flexible printed wiring sheets are, for example, mechanically connected through a sheet connector. However, in this case, there is a drawback that the sheet connector is required as additional equipment. Also, there is another drawback that it is difficult to make up a thin and miniaturized type of electronic apparatus because the sheet connector is not thin and comparatively large.
To solve the above drawbacks, there is still another conventional method in which the simple type of flexible printed wiring sheets are pressed to mechanically connect with one another through an anisotropic conductive coated film by utilizing a heated rubber which is wound up around the sheets. In this case, the anisotropic conductive coated film is sealed between the sheets to electrically connect the electronic wiring networks with each other.
2.1. Previously Proposed Art
A conventional method for electrically connecting wirings printed on flexible wiring sheets through an anisotropic conductive coated film is described with reference to FIGS. 1 & 2.
FIG. 1 is a diagonal view of a connecting section in which insulating sheets and an anisotropic conductive sheet positioned between the insulating sheets are arranged according to a conventional method.
FIG. 2A is a sectional view of the connecting section shown in FIG. 1 in which the anisotropic conductive sheet is sandwiched by wirings printed on the insulating sheets, the wirings being not electrically connected with each other.
FIG. 2B is a sectional view of the connecting section shown in FIG. 1 in which the wirings printed on the insulating sheets are electrically connected with each other through the anisotropic conductive sheet compressed by the insulating sheets.
As shown in FIG. 1, an upper pattern of wirings 11 is printed on an upper insulating sheet 12, and a lower pattern of wirings 13 is printed on a lower insulating sheet 14. Also, an anisotropic conductive sheet 15 is arranged between the upper and lower insulating sheets. The upper and lower insulating sheets 12, 14 and the anisotropic conductive sheet 15 are arranged at a connecting section of flexible printed wiring sheets. In addition, an electric wiring network drawn in one of the flexible printed wiring sheets is electrically connected with the upper wirings 11. Also, another electric wiring network drawn in the other flexible printed wiring sheet is electrically connected with the lower wirings 13.
Thereafter, as shown in FIG. 2A, the anisotropic conductive sheet 15 is sandwiched by the upper and lower insulating sheets 12, 14 through the upper and lower wirings 11, 13. Thereafter, a heated rubber (not shown) is tightly wound up around the upper and lower insulating sheets 12, 14 to press the anisotropic conductive sheet 15. Therefore, the anisotropic conductive sheet 15 is softened by the heat applied by the heated rubber. As a result, as shown in FIG. 2B, parts of anisotropic conductive sheet 15 directly sandwiched between the upper and lower wirings 11, 13 are thinned by the heated rubber. Thereafter, the heated rubber is taken off from the upper and lower insulating sheets 12, 14 so that the anisotropic conductive sheet 15 deformed by the heated rubber is hardened. That is, the upper and lower insulating sheets 12, 14 are mechanically connected through the thinned anisotropic conductive sheet 15. As a result, a pair of connected sheets 16 is made up.
In addition, in cases where the anisotropic conductive sheet 15 is pressed in a direction, the electric resistance of the anisotropic conductive sheet 15 is considerably reduced in the direction because the sheet 15 has anisotropic property.
Accordingly, because the parts of anisotropic conductive sheet 15 directly sandwiched between the upper and lower wirings 11, 13 are pressed, the electric resistance between the upper and lower wirings 11, 13 is considerably reduced so that the upper and lower wirings 11, 13 are electrically connected with each other.
Therefore, a thin and miniaturized type of electronic apparatus can be easily manufactured by utilizing the anisotropic conductive sheet 15.
However, in the above conventional method, the anisotropic conductive sheet 15 is required to make up the connected sheets 16. However, the anisotropic conductive sheet 15 is very expensive because the sheet 15 has anisotropic property. Therefore, there is a drawback that the wirings 11, 13 cannot be electrically connected at lower cost.
In addition, because the heat is transferred from the heated rubber to the anisotropic conductive sheet 15 through the wirings 11, 13, it takes a lot of time to deform the anisotropic conductive sheet 15. For example, it takes from twenty seconds to one minute. Therefore, the connected sheets 16 cannot be rapidly made up. As a result, there is another drawback that the electronic apparatus cannot be manufactured on a large scale.